There are believed to be rain sensors for motor vehicles including windshield-wiper devices. These devices including a measuring element, which has a sensitivity that is predefinable by a control device. For instance, German Published Patent Application No. 197 23 859 refers to a rain sensor in which day and night may be distinguished with the aid of a photocell and the triggering sensitivity of the rain sensor is controlled. Furthermore, the sensitivity of the measuring element of the rain sensor may be varied as a function of the detected signal, and, thus, the rain intensity.